The filling of bottles is generally classified in two categories, i.e. level filling and volumetric filling, depending on the technology used to detect when the right amount of liquid supplied has been reached. In turn, level filling differs depending on the liquid to be processed. In the case of non-gaseous liquids filling is performed at atmospheric pressure or under a slight vacuum, in the case of gaseous liquids an isobaric filling is performed and in the case of viscous liquids filling is performed under conditions where there is a pressure difference, obtained by creation of high vacuum or by overpressure.
The filling device according to the present invention falls within the category of level-filling devices, and more precisely devices of the type performing isobaric level filling (hereinafter simply referred to as “isobaric filling”).
FIG. 1 of the accompanying drawings shows an axially sectioned view of a known example of a filling device for an isobaric filling machine. The filling device is denoted overall by 10 and comprises essentially:                a body 12 intended to be fixed to a bottom wall 14 of a tank 16 of a filling machine, the body 12 having an inner cavity 18 which is open at the top and communicates at the bottom with the outside by means of a nozzle 20 with a conical cross-section which is fixed to the body 12 and the axis z of which is oriented vertically;        a first tube, or outer tube, 24 which is fixed to the top part of the body 12 and is arranged coaxially with the nozzle 20, passing, in the assembled condition of the filling device on the filling machine, through a hole 22 in the bottom wall 14 of the tank 16 and extending up to a certain distance from the bottom of the tank;        a second tube, or inner tube, 26 which is arranged coaxially with the nozzle 20 and the outer tube 24, extending inside the outer tube 24 and emerging at the bottom from the body 12 through the nozzle 20;        a centring cone 28 which is arranged coaxially with the nozzle 20 and the inner tube 26 and is provided with a seal member 30 for sealing against the top end of the neck of a bottle (not shown) to be filled; and        a valve assembly 32 comprising a plurality of valves 34 (in the example shown three valves) intended to be controlled by means of cams suitably configured to start and stop the various steps provided for by the bottle filling cycle.        
The filling device 10 also comprises a closure member 36 (referred to below as first closure member) which is provided with a seal member 38 and is fixed to the inner tube 26, coaxially therewith, so as to cooperate with a conical surface portion 40 of the inner cavity 18 of the body 12. The inner tube 26, and together therewith the first closure member 36, is movable with respect to the assembly formed by the body 12 and by the outer tube 24 between a lowered position (shown in FIG. 1), in which the first closure member 36, by means of the seal member 38, closes off the passage from the inner cavity 18 to the nozzle 20, and a raised position (not shown), in which an annular passage is created between the first closure member 36 and the conical surface portion 40 of the inner cavity 18, through which passage the liquid which flows from the tank 16, through one or more openings 42 provided in the outer tube 24, to the annular conduit 44 defined between the outer tube 24 and the inner tube 26 may flow out towards the nozzle 20 and from here into the bottle. The first closure member 36 is pushed towards the raised position by a spring 46 arranged between a snap ring 48 mounted on the outer tube 24 and an abutment member 50 fixed to the top end of the inner tube 26.
The filling device 10 also comprises a second closure member 66 which is positioned coaxially with the inner tube 26, above the latter, and is movable axially with respect to the inner tube 26 between an open position (position shown in FIG. 1), in which it is at a distance from the top end of the inner tube 26 and therefore leaves this tube open, and a closed position (not shown), in which it makes sealing contact with the top end of the inner tube 26 and therefore keeps this tube closed.
In the case of gaseous liquids, and more particularly in the case of sparkling wine, the bottle filling cycle with a filling device such as that of the known type shown in FIG. 1 comprises typically the steps described below.
First of all, the bottle to be filled is raised by means of a pneumatic piston so as to be pressed against the seal member 30 of the centring cone 28 until the centring cone 30 comes into contact against the body 12 around the outlet section of the nozzle 20, so as to provide a perfect seal between the body and the bottle in order to contain the filling pressure.
This is followed by a deaeration step, during which the air contained inside the bottle is forced out of it by means of a liquid-ring vacuum pump (not shown).
Then the bottle is put in communication with the portion of the tank 16 situated above the level L of the liquid through the inner tube 26 (with the second closure member 66 in the open position) in order to carry out the pressure compensation step, during which the gas under pressure contained in the tank passes from the latter into the bottle until the gas contained in the tank and the gas contained in the bottle are at the same pressure.
Once a balance between the pressure of the gas in the tank 16 and the pressure of the gas in the bottle is reached, the spring 46 causes raising of the inner tube 26, and together therewith of the first closure member 36, thus allowing the liquid contained in the tank to fill the bottle passing through the annular passage defined between the nozzle 20 and the inner tube 26 (filling step). During filling of the bottle with the liquid, the gas previously introduced into the bottle returns into the top portion of the tank 16 flowing inside the inner tube 26. When the level of the liquid in the bottle has reached a given predefined value, the assembly formed by the inner tube 26 and by the first closure member 36 is moved into the lowered position so as to interrupt the flow of fluid from the tank into the bottle. The filling step is then followed by a levelling step during which gas under a slight overpressure (about 0.2 bar greater than the pressure present in the bottle) is introduced into the bottle through the annular passage defined between the nozzle 20 and the inner tube 26, with the first closure member 36 remaining in the lowered position, so that the excess liquid contained in the bottle, i.e. the liquid which is situated above the bottom end of the inner tube 26, is conveyed back into the tank 16 through this tube.
This is followed by a degassing step during which the inside of the bottle is put in communication with the outside so as to eliminate slowly the overpressure produced during the previous step.
Finally, the pneumatic piston is lowered so as to allow removal of the bottle which has now been filled.
The main drawback of the known filling devices for isobaric filling machines, such as that described above with reference to FIG. 1 or that known from the aforementioned prior document, consists in the poor precision in the bottle filling level. This is due in particular to the fact that, when the first closure member with the associated seal member closes off the flow of the liquid towards the bottle, the liquid which is already present between the nozzle and the inner tube downstream of this closure member enters into the bottle and therefore increases the filling level of the bottle with respect to that desired. The levelling step described above is therefore required, this resulting in a considerable amount of liquid flowing back into the tank and therefore in an increase in the danger of contamination of the liquid in the tank. Moreover, once the inner tube has been closed by means of the second closure member, any liquid contained inside this tube may return into the bottle and therefore modify the (correct) filling level reached.
A further drawback of the known isobaric filling devices is that adjustment of the filling level is obtained by displacing vertically the inner tube (gas return tube), which results in these devices being particularly complex.
Moreover, the known isobaric filling devices are all provided with a certain number of springs in order to ensure that the pressure levels are balanced and perform opening or closing of the closure members, this resulting in these devices being constructionally even more complicated and creating greater problems during washing and sterilization, in view of the large surface area of the springs exposed to contact with the liquid.